1 Introduction:
Municipal Landfills are the final resting and hiding place for all of our garbage. Landfills cost millions of euros to build and tens of euros to maintain. They often leak, spilling toxic fluids that contaminate groundwater. Paper can take well over 160 times longer to decompose in a landfill. They fill up after only about 7 years, but must be maintained for 30 years. They are a massive polluter to groundwater and are a leading contributor to global warming. But still we are maintaining them. Where else can we put all those wastages?
1.1 Background:
Today municipal solid waste is an accumulating problem with increased urbanisation. About ten million people live in Dhaka city, the capital of Bangladesh. Estimates for solid waste generated in Dhaka city varies from 3,000 to 3,500 tons per day. The wastes are highly diverse in nature and encompass a variety of materials including household refuse, mining, industrial by-products and street sweepings. The disposal of solid waste produced in Dhaka city is calculated to require 110 hectares of land per year. With further increase in population, the amount of solid waste will also increase proportionately. It is expected that by the year 2015, the total waste created in Dhaka city will be about 8,000 tons per day, requiring about 292 hectares of land for disposal. Bangladesh, a land-scarce country, does not have such physical space (Sinha et. al., 1997). As long as the population to grow the need for more disposal sites will grow. The indiscriminate disposal of solid waste in landfills causes serious environmental hazards and health risks. Flies, cockroaches and rodents thrive in landfills, and they are the known sources of many diseases. Uncontrolled wastes in landfills also clog the urban drainage system, cause frequent floods and contaminate drinking water sources. Thus, the growing problem of solid waste dumping in landfills is posing increasing threats to the health and well being of the residents.
1.2 Problems associated with landfills
1.2.1 Drinking water contamination:
Leachate is water that gets badly contaminated by contacting waste ( Quasim S.R.et. al.,1994),. Municipal landfill sites produce leachate when rain, surface or ground water enters into the landfill site. Leachate contains a wide range of toxic substances arising from the decomposition of waste, and causes contamination of domestic groundwater sources and deterioration of water ecosystems through oxygen depletion (eutrophication) of watercourses. Leaking landfills pollutes drinking water wells with cancer-causing chemicals such as toluene or vinyl chloride and have harmed many communities.
Sources of leachate are generated in the municipal waste dumping sites in large cities. Also considerable amounts of industrial leachates are generated from industrial sources. In Dhaka city, and all other big cities of the country, municipal wastes are dumped in low-lying landfills. Municipal leachates are rich in chlorinated hydrocarbon solvents (CHS), which are very toxic and carcinogenic. Recent investigations have found remarkable quality deterioration under landfill leachates and identified a number of CHS in groundwater from the industrial areas (Bernard B et. al. 1973). It is very likely that the same contaminants may also be present in groundwater in other large cities and industrial zones of Bangladesh. The picture is also the same in the developed countries of the world. In a recent study of 163 municipal waste landfills in the U.S.A, there was evidence of contamination rate for ground water quality at 146 of them (NORTHWEST, 2010). That’s a 90% contamination rate for ground water beneath municipal solid wasteland fills. Once ground water is polluted it is almost impossible to clean it up.
1.2.2 Global Warming:
Biodegradable garbage rotting in a landfill produces methane gas—a ‘greenhouse gas’ that contributes to global warming. Methane is 21 times more potent in its greenhouse effect than carbon dioxide (from car exhaust), and landfills are the largest man-made source of methane (37% globally).
1.3 How landfills are constructed and why they fail?There are three critical elements in a secure landfill: a bottom liner, a leachate collection system, and a cover (ZERO WASTE AMERICA, 2010) as described below:
Figure: Section of a Landfill. Source: (GETSTUFF, 2010)
What is a bottom liner?
It may be one or more layers of clay or a synthetic flexible membrane (or a combination of these). The liner effectively creates a bathtub in the ground. If the bottom liner fails, wastes will migrate directly into the environment. There are three types of liners: clay, plastic, and composite.
What is wrong with a clay liner?Natural clay is often fractured and cracked. A mechanism called diffusion will move organic chemicals like benzene through a three-foot thick clay landfill liner in approximately five years. Some chemicals can degrade clay.
What is wrong with a plastic liner?
The very best landfill liners today are made of a tough plastic film called high-density polyethylene (HDPE). A number of household chemicals will degrade HDPE, permeating it (passing though it), making it lose its strength, softening it, or making it become brittle and crack.
What is wrong with composite liners?
A Composite liner is a single liner made of two parts, a plastic liner and compacted soil (usually clay soil). Reports show that all plastic liners (also called Flexible Membrane Liners, or FMLs) will have some leaks. It is important to realize that all materials used as liners are at least slightly permeable to liquids or gases and a certain amount of permeation through liners should be expected. Additional leakage results from defects such as cracks, holes, and faulty seams. Studies show that a 10-acre landfill will have a leak rate somewhere between 0.2 and 10 gallons per day.
What is a leachate collection system?
Leachate is water that gets badly contaminated by contacting wastes. It seeps to the bottom of a landfill and is collected by a system of pipes. The bottom of the landfill is sloped; pipes laid along the bottom capture contaminated water and other fluid (leachate) as they accumulate. The pumped leachate is treated at a wastewater treatment plant. If leachate collection pipes clog up and leachate remains in the landfill, fluids can build up in the bathtub. The resulting liquid pressure becomes the main force driving waste out the bottom of the landfill when the bottom liner fails.
What are some of the problems with leachate collection systems?
Leachate collection systems can clog up in less than a decade. They fail in several known ways:
1. They clog up from silt or mud;
2. They can clog up because of growth of microorganisms in the pipes;
3. They can clog up because of a chemical reaction leading to the precipitation of minerals in the pipes; or
4. The pipes become weakened by chemical attack (acids, solvents, oxidizing agents, or corrosion) and may then be crushed by the tons of garbage piled on them.
1.4 What can we do to reduce pressure on landfills?
Landfills are outdated technologies that do not have a place in the 21st century. However, vested interests are still promoting them as safe waste management solutions. No matter what technologies are available, we can all help by reducing the amount of waste that we generate. The main motivations for waste reduction are frequently related to the high cost and scarcity of sites for landfills. The places that currently do not have significant disposal pressures can still benefit from encouraging waste reduction.
1.4.1 Key concepts in municipal waste reduction
1.4.1.1 CLEANER TECHNOLOGY
Industries should use processes that make the least possible waste. This is called using Cleaner Technology. It is always best to avoid creating waste in the first place. To avoid creating waste we should (Ljiljana R., 2000 ;Maksimovic C. et. al., 2001; Sinha et. al., 1997):
• Buy only what we need and can use
• Avoid extra packaging
• Separate wastes such as paper, tins and bottles for recycling or re-use.
Industries should be encouraged to:
• Check that machinery is working properly
• Use less raw materials
• Recover and recycle waste wherever possible
• Reduce toxicity of the waste
• Use only necessary packaging
• Train staff to avoid mistakes that cause waste, such as spilling of oil or chemicals.
1.4.1.2 REUSE
We should:
• Consider reusable products
• Maintain and repair durable products
• Reuse bags, containers, and other items
• Borrow, rent, or share items used infrequently
• Sell or donate goods instead of throwing them out.
1.4.1.3 RECOVER AND RECYCLE
Anything that can be used again should be taken out of the waste. This is called recycling or Resource recovery. We can take useful items out of our waste and use them again, for example:
• old engine oil and car batteries can be taken back to the garage for recycling
• tins, bottles and paper can be taken to recycling bins
• vegetable peels can be made into compost
And also we should:
• Choose recyclable products and containers and recycle them
• Select products made from recycled materials.
Any improvements in waste management standards will always cost more. The person or industry that makes the waste must pay these costs. It is only fair that the waste generator or polluter should pay the cost of waste management and not the community. This is known as the polluter pays principle. After all it is the community that suffers if waste is not properly managed. Increased disposal and clean up costs will also encourage the waste generator to use cleaner technology and to reduce the waste generation as much as possible.
1.5 Conclusion
There is no debate that all landfills eventually contaminate our environment. It is expected that in future, municipal solid waste management practices will greatly emphasize in resource recovery, and solid waste reduction. Modern techniques with energy recovery will play an important role in waste reduction and energy conservation. So alternatives to land filling would have environmental effects which include: resources for the future, jobs from discards, more open space and natural habitat, less contamination of drinking water and soil improvement to assist agriculture in fertile soil.
References:
1. Bernard B, Charles H. P., DeBell and Richardson (1973), “Solid waste Disposal, vol-1, incineration and landfill”, 1st edition, Michigan, USA
2. GETSTUFF (2010), “How Landfills Work”, [On Line] http://science.howstuffworks.com/landfill6.htm [15th May, 10]
3. Maksimovic C., Jose A.T.G. (2001), “Frontiers in urban Water Management, Deadlock or Hope” 2nd edition, IWA publishing, London, UK
4. NORTHWEST INDIANA (2010), “Landfills in Northwest Indiana”, [On Line] http://www.iun.edu/~environw/landfills.heml [2nd March, 10]
5. Ljiljana R., (2000), “Reliability of Landfill Technology”, 1st edition, Uitgeverij Eburon, Delft, The Nethelands
Quasim S. R., Walter C.(1994), “Sanitary landfill leachate, generation control, treatment”, 1st edition, Technomic Publishing Company, USA
6. Sinha and Enayetullah, 1997, “Waste as resource.” Article in The Bangladesh Observer, Dhaka, November 21, 2001.
7. ZERO WASTE AMERICA (2010), “The basics of landfills: How they are constructed and why they fail”, [On Line] http://www.zerowasteamerica.org/BasicsOfLandfills.htm [12th March, 10]
Terms
Groundwater: Water that infiltrates into the Earth and is stored in usable amounts in the soil and rock below the Earth’s surface; water within the zone of saturation.
Leachate: A liquid that results from water collecting contaminants as it trickles through wastes, or soil containing agricultural pesticides or fertilizers
Percolate: To drain or seep through a porous and permeable substance; to filter such as a liquid passing through a porous body (water through soil to the aquifer)
Residue: Something that remains after a part is taken away
We are thankful to Barua R. (Public Works Department (PWD),Bangladesh) and Naz N.N. (Local Government Engineering Department(LGED), Bangladesh) for sharing this information with us on engineeringcivil.com. We hope this would be of great significance to civil engineers.
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